1. FIELD OF THE INVENTION
This invention relates to cardiac valvular surgery techniques for replacement of diseased cardiac valves. More particularly, this invention relates to materials and techniques for replacement of diseased mitral valves in humans as well as other animals.
2. PRIOR ART
Cardiac valvular surgery is performed in cases where there is a diminished flow area within a cardiac valve which results in a blockage of normal flow. This blockage leads to cardiac failure. Cardiac valvular surgery may also be required in cases of valvular incompetence in which back flow of blood occurs across a valve that cannot close fully. This is also known as valvular regurgitation Each of the above conditions are frequently due to rheumatic heart disease. Replacement of stenotic or narrowed cardiac valves and regurgitant or incompetent cardiac valves requires open-heart surgery which utilizes a heart-lung machine.
Expansible devices for implantation have been known by the medical community. These devices include, for example, the so-called recovery metals such as titanium-nickel equiatomic intermetallic compounds which demonstrate mechanical "memory" whereby after being formed into specific shapes, these metals are compressed or otherwise given temporary different shapes for insertion and thereafter, when in place, are expanded whereby their mechanical "memory" of the originally formed shape causes the device to assume its originally formed shape.
Materials which are known for having properties useful in such systems include nickel based alloys such as those described in U.S. Pat. No. 3,174,851. Typically, these materials comprise 52 to 56 percent nickel by weight with the remainder being titanium. An initial shape may be permanently set into such recovery metals by heating them while they are held in the desired configuration. The forming temperature for setting the initial shape into the described titanium-nickel alloy is typically about 930.degree. F. The alloy is then cooled and thereafter deformed plastically to a deformed configuration which can be retained until the alloy is reheated to a transition temperature whereafter the alloy will recover its initial configuration.
Various implantable appliances have been described in the patent literature. For example, U.S. Pat. No. 3,868,956 uses an expansible appliance implanted with a vessel through a catheter involving a positioning device. The positioning device is complex because it requires the use of electrical conductors to heat the expansible appliance to allow it to function. U.S. Pat. No. 4,503,569 positions and expands a graft prosthesis using hot saline.
Generally, the known art applies these techniques to the repair of blood vessels narrowed or occluded by disease.
If a satisfactory means could be devised of replacing diseased cardiac valves percutaneously, many major open-heart surgeries could be avoided.